The present invention relates generally to the field of printing and more specifically, the control of the exposing light.
Photopolymer plate material is available for use for printing images. The plate is photo sensitive to ultraviolet light. Thus, a photonegative is placed between the ultraviolet light source and the photopolymer plate with the ultraviolet light cross links the polymers thereby hardening the image on the plate.
The image on the plate consists of a plurality of pedestals onto which the ink is transferred for printing. A typical prior art photopolymer plate cross section is shown in FIG. 1 illustrating the upraised pedestals 11 having a top ink receptive surface 12 and a downwardly sloping side surface 13 surrounding the pedestal and providing a generally truncated conical configuration for the pedestal. Side surface 13 terminates in a trough 14 extending between the adjacent pedestals, for example, pedestal 11 and 15.
Pedestal side surface 13 is formed by shining ultraviolet light through the film negative and onto plate 10. The bevel angle 16 between side surface 13 and the top surface 12 of the pedestal is relatively small since the ultraviolet light rays are directed against the photopolymer plate at various angles. Thus, side surface 13 is not steep.
Pedestal 11 may be compressed when contacted by an ink roller transferring the ink not only onto surface 12 but also onto side surface 13. When the photopolymer plate is used to transfer the image onto an external surface, the pedestals may again be compressed thereby transferring the ink not only from surface 12 but also surface 13 onto the external surface thereby leaving a ring around the image formed on the final copy composed of the image from the various top surfaces 12 of the various pedestals. The net results is final copy that does not have a sharp and clear image.
In order to provide a sharp clear image, it is desirable to increase angle 16 thereby orienting side surface 13 at a steep angle relative to top surface 12 minimizing any image transferred by the side surfaces 13. Various attempts to provide a steep side surface 13 have tried through the use of multiple ultraviolet light sources positioned above the photopolymer plate Nevertheless, each light source emits rays at a variety of angles with the ultraviolet light still striking the photopolymer plate at different angles. Disclosed herein is a device and method for directing the ultraviolet light perpendicularly against the photopolymer plate.
One embodiment of the present invention is a combination for use in producing sharp printed images comprising a source of light and a panel positioned to receive the light with the panel containing the image to be printed. A photopolymer printing plate is positioned relative to the panel to receive the light passing therethrough. A collimating filter is positioned relative to the panel and the plate to limit passage of light from the panel onto the plate to substantially parallel rays of light.
Another embodiment of the present invention is a method of transferring an image on a panel onto a printing plate comprising the steps of providing a photopolymer printing plate, aligning a panel having an image thereon with the plate, shining light onto and through the panel to shine onto the plate, and directing the light into rays of light substantially perpendicular to the printing plate exposing the plate.
It is an object of the present invention to provide a photopolymer plate for producing sharp printed images through the use of printing pedestals having steep side surfaces.
A further object of the present invention is to provide an ultraviolet light filter in combination with a photopolymer plate to limit the angle the ultraviolet light strikes the photopolymer plate.
A further object of the present invention is to provide a new and improved method of providing an image on a printing plate.
Related object and advantages of the present invention will be apparent from the following description.